Good-day,
I was observing the PWM signal coming out of the Motor controller-29 using an oscilloscope. I realised that above a PWM value of 90, the signal went completely crazy.There was a lot of noise on the signal and I was not even able to observe the PWM period.
I was able to observe the PWM signal for all other PWM values. Is there some reason for this? I tried it with two(2) of these controllers and the same thing occurred. So that ruled out the possibility of faulty components.
Thanks.
Also, I am not exactly seeing what that motor controller is doing when used with the 2-wire motors. The three wire motor ports on the Cortex has a PWM signal pin and then I plug in the motor controller into that and then send to the motor. So, what exactly is that doing?
Thanks.
Have you read the multitude of recent threads discussing motors?
https://vexforum.com/t/motor-torque-speed-curves/21602/1
https://vexforum.com/t/vexpro-motor-speed-tests/21688/1
https://vexforum.com/t/cortex-motor-speed-testing/21687/1
The motor controller turns the RC servo pwm signal into a variable duty cycle pwm signal suitable for controlling the motors speed. It’s a difficult signal to observe due to the inductive nature of the motor and the back emf it generates.
PWM doesn’t come out of the motor controller 29 it goes in… 
Interesting that 90 is special though. How/where are you taking the measurements?
PWM seems like a good description of mc#29 output.
How else would you describe picture 3 of post 1 of this thread?
Unfortunately “PWM” has different meanings for the input and output signals of the MC29. On the input side the pulse will change in width from 1mS to 2mS (well actually 0.86mS to 2.14mS on the MC29 but that’s another story) in duration and will repeat every (approx) 20mS. On the output side the pulse width will vary from 0 to (approx) 800uS with a frequency of 1200Hz, ie. it is a 1200Hz square wave with a duty cycle that changes from 0 to 100%.
Interesting. The PWM outputs from Cortex motor ports 2 thru 9 are just control signals. This PWM just tells the downstream electronics (either in the 3-wire motor or in the MC29) which direction to turn the motor and how much power (basicly what average voltage) to apply to the motor.
Cortex motor ports 1 & 10, as well as the MC29 output, provide variable power and voltage polarity (motor direction) directly to the 2-wire motors. In general, zero percent PWM is zero power and 100% PWM is full power.
So, is your MC29 not providing full power? Maybe and maybe not. Ninety percent of full power may just be a limitation of the circuitry in every MC29. An interesting experiment would be to compare the MC29 output characteristic to that of motor ports 1 and 10. The output delivering the highest PWM percent is the best power source for your most critical motor application.
As a sanity check, you could repeat the output measurements using a DC voltmeter. The meter should roughly average the PWM voltage waveform and provide a reading that is roughly proportional to the duty cycle percent observed on the scope.
Gentlemen, I don’t mean this to sound arrogant but please read the threads I referenced for you all. This thread in particular has some fairly in depth explanation as to why the MC29 reaches 100% duty cycle when commanded with an input value of somewhere around 85 or 90. I also posted graphs showing the difference between port 1&10 and the 3 wire ports. I do encourage you all to do your own experiments but this has all been discussed recently with some interesting input from the folks at VEX who have shared some of their own test results with us.